Advancements in technology and the growing concern for environmentally efficient vehicles have led to the use of alternate fuel and power sources for vehicles. Electric vehicles or hybrid electric vehicles use electro mechanical devices (motors) to power the vehicle. In order to provide the required torque and power to operate the vehicle the motor must be designed to operate over a broad operating range. When a motor is chosen to act for an all purpose function, such as driving a vehicle, the motor needs to have the capacity for all load conditions, including the capacity to meet the maximum torque and power demands of the vehicle.
However, vehicles do not require peak torque and power at all times of operation. During normal operating conditions there is excess torque and power available from the motor. Additionally, motors, like any power source, have certain efficiency ranges in which they achieve their optimal performance. Sizing the motor to provide the capacity for all load conditions results in an over-sized motor that must bear the inefficiency when not operating at the optimum range. Inefficiencies of the over-sized motor are most apparent when operating at low speed. At low operating speed the forces to overcome the mass of the rotor contributes to great inefficiencies. Another inefficiency from an oversized motor is, the centrifugal forces required to start and stop the motor requires excess power and depletes the available energy more than necessary.
Additionally, vehicles are available in a variety of sizes and weights which results in additional variety in the motor capacity required among various vehicles. Therefore, the larger vehicles must default to larger and unique motors. The cost to design, manufacture and carry inventory on the variety of motors required results in cost inefficiencies as well.